Last weekend, President Donald Trump argued that those foreigners who enter the United States unlawfully should simply be taken to the border, escorted across it and let go. According to the president, this would save precious government resources, avoid the business of separating children from their parents and free up the Border Patrol and other federal assets to do their jobs.

He is undoubtedly correct on the beneficial consequences to the government of forced deportation without due process. Yet deportation without a trial is profoundly unconstitutional.

Here is the back story.

The nation has been torn apart by the images of immigrant children -- some are babies -- being forcibly separated from their parents by U.S. immigration authorities, who were getting orders from the Trump administration, which was misreading federal law so as to require the separation.

The government has essentially taken the position that those physically present in the U.S. illegally have few constitutional rights and thus family members who arrive together can be separated, no matter the psychological or physical consequences. This forced separation is not novel to the Trump administration, but its massive scale in the present toxic national political environment has painfully brought it to our collective conscience.

The forced separation by the government of children from their parents without a trial when neither is a danger to the other is child abuse or kidnapping or both. When federal authorities engage in such morally repellant behavior -- whether as a negotiating technique to bring the president's political adversaries to the bargaining table or to coerce the immigrants to go home -- it exposes them to state prosecution because of the acute and long-term harm they have caused to the children.

After a tidal wave of public opinion against this practice finally resonated in the White House, President Trump signed an executive order last week that permitted, but did not require, immigration authorities to reunite the children and their parents. Then, in the wake of a slow reunification -- some of the children had been sent from Texas to New York while their parents were kept in Texas -- the president uttered his exasperation regarding due process.

If he had asked his lawyers first, he would have learned that there is no legal basis for his official antipathy to due process.

The president took an oath to preserve, protect and defend the Constitution. The Fifth Amendment to the Constitution provides in relevant part that "no person shall be ... deprived of life, liberty, or property, without due process of law." This is the so-called Due Process Clause, and it essentially prevents all governments from impairing the life, liberty or property of any human being on American-controlled soil without a fair trial.

Because the Supreme Court has ruled that there are no word choice errors in the Constitution and the words of its text mean what they say, the Framers must have carefully and intentionally chosen to protect every person, not just every citizen. "Person," in this context, has been interpreted to mean any human being on American-controlled soil against whom the American government is proceeding, irrespective of how the person got there.

This protection is so profound and universally understood that when the George W. Bush administration rounded up what it thought were the collaborators, enablers, supporters and relatives of the 9/11 murderers whom it thought were here unlawfully, it recognized their due process rights and afforded them trials before deportation. The government actually lost many of those cases, and innocents were not deported.

Hundreds of books and law review articles have been written about due process. Here we are addressing procedural due process, which has three components. The first is notice. The person against whom the government is proceeding is entitled to a written statement specifically articulating his alleged wrongful behavior sufficiently prior to trial. Once notice is given, the government is hard-pressed to alter the charges.

The second component of due process is the requirement of the government to prove its charges against the person to whom it has given notice before a neutral judicial official, not one who works for the entity that is proceeding against him.

The third component of due process requires that the entire proceeding against the person be fair, that it appear to be fair and that the outcome be rational. The judge can decide whom to believe, but she cannot, for example, decide that 2+2=22, as that would be irrational. Fairness also includes the right to an appeal.

The dangers of rejecting the plain meaning of the Constitution ("person") and the dangers of taking a class of people and refusing to recognize their fundamental constitutional rights because of an immutable characteristic of birth (alienage) cannot be overstated.

President Trump is my friend. I like him dearly and wish him well and want him to succeed. But he is profoundly wrong here. He cannot lawfully or morally reject his oath to uphold the Constitution. Denying due process on the basis of alienage is tantamount to denying the personhood of undocumented foreigners as the U.S. once did to slaves and does today to babies in the womb. And that denial is a slippery slope, at the bottom of which lie tyranny and misery.